The present invention relates to an optical switch for switching over connection of an optical signal transmitted through a plurality of optical fibers. In particular, the present invention relates to an optical switch for switching over the direction of the collimated optical signal by using a mirror.
Until now, a large number of optical switches have been proposed.
As a mechanical optical switch, an optical switch of optical fiber drive type having a structure which directly drives a magnetic film added to an input optical fiber by using a magnetic coil and which switches over one output optical fiber to another output optical fiber is proposed (see JP-A-2001-154124, pages 4 to 5 and FIGS. 1 to 3).
With the object of implementing a large scale optical switch, an optical switch according to an optical cross connect technique of three-dimensional free space type utilizing the MEMS (Micro Electro Mechanical System) technique is proposed (for example, see JP-A-2001-174724, pages 3 to 4 and FIG. 2). The optical switch of the three-dimensional free space type includes optical fibers, collimator lenses and mirror arrays.
FIG. 12 is an oblique view showing an example of a structure of a conventional optical switch. A light beam 103 formed by being passed through an input side optical fiber 101 and an input side collimator lens 102 is reflected by an input side mirror array 104, reflected again by an output side mirror array 105 opposed to the input side mirror array 104, passed through an output side collimator lens 106, and input to an output side optical fiber 107.
The light beam 103 is switched by changing positions of mirror devices 108 provided in the input side mirror array 104 and the output side mirror array 105 and causing reflection.
FIG. 13A is an X-Y plane view showing a structure of the mirror device 108 shown in FIG. 12. FIG. 13B is an X-Z sectional view showing the structure of the mirror device 108. The mirror device 108 has a structure in which a movable mirror 109 which reflects light into midair and which inclines is supported by a plurality of beams so as to be able to swing.
Various methods for inclining the movable mirror 109 have been contrived. Inclination caused by electrostatic force is used most frequently. In that case, electrodes 112 are formed on the movable mirror 109, and a plurality of electrodes 111 are formed in positions nearly opposed to the electrodes 112.
The movable mirror 109 includes an inner mirror 109a and an outer mirror 109b. The inner mirror 109a is coupled to the outer mirror 109b by a pair of beams 110. The outer mirror 109 is coupled to a substrate by a pair of beams 110.
Surfaces of the inner mirror 109a and the outer mirror 109b are coated with reflecting films 113 for reflecting a light beam. In general, gold, which has a high reflectance, is used as the reflecting films 113. Electrostatic drive electrodes 112 are formed on opposite faces of both the inner mirror 109a and the outer mirror 109b from the reflecting films.
Four separate electrodes 111 are formed in positions nearly opposed to the electrodes 112 in order to incline each of the inner mirror 109a and the outer mirror 109b in two directions. A voltage is applied between the electrodes 111 and the electrodes 112 to twist the beams 110 by using the electrostatic force, incline the movable mirror 109, and maintain a predetermined position.